Bacterial infections, particularly bovine mastitis, are the most costly, complex and difficult challenge to the dairy industry. In the United States alone, mastitis costs dairy farmers close to $3 billion a year, or about $300 per cow.
Mastitis is defined as an inflammation of the mammary gland, and occurs primarily as a result of infection by bacteria which gain entry to the udder via the teat canal. Mastitis is recognized to exist in two forms, "subclinical," where the infection is not directly evident by visual or physical inspection of either the milk or the mammary gland, and "clinical," which is diagnosed by the presence of visually detectable alterations in the milk (clots, discoloration) and glands (swollen, firm, warm, painful). Elevated levels of white cells in the milk, in response to the infection, are characteristic of mastitis. The common demarcation of 500,000 white cells per milliliter of milk separates "subclinical" and "clinical" mastitis.
It has been estimated that about 20 cases of subclinical mastitis occur for every case that, untreated, generally develops into overt clinical mastitis. Both subclinical and clinical forms affect milk production. Depending on the severity of the subclinical form, the production of milk by an infected cow can be as much as 20% less than that of a non-infected cow, and cases of subclinical disease can last for several months. On the other hand, the milk from a clinically-mastitic cow must be discarded, and in some cases the cow has to be destroyed (if the disease resists treatment). The cow may even die, often within 24 hours, following infection with certain coliform organisms.
Prior attempts to treat the mastitis infection have involved the infusion of an antibiotic into the udder (in the case of the clinical disease). Since treatment is commonly instituted prior to identification of the specific causative organism, it is important to select an antimicrobial which offers the greatest range of efficacy against the array of pathogens causing mastitis. Although certain organisms, such as Streptococcus agalactiae and Staphylococcus aureus, are the principle pathogens associated with infectious mastitis, a great number of environmental and contagious microorganisms are also known to cause this disease (e.g., coliforms, Klebsiella pneumoniae, Actinomyces pyogenes, Corynebacterium bovis, Listeria monocytogenes, Pseudomonas aeruginosa, other Staph. and Strep. species, and Mycoplasma bovis).
Despite a recognized need, no single antibiotic is presently available to the dairy industry that has demonstrated activity against all the mastitis associated organisms. Furthermore, all current antibiotic therapies for mastitis, which involve infusion into the infected quarter of the udder, result in a mandatory time period thereafter in which the cow's milk cannot be sold. This occurs because these antibiotics can remain in the cow's udder for many days after infusion, and contaminate the milk produced during that time. This contamination will significantly inhibit the growth of microorganisms in milk, particularly those used for processing the milk into cheese or yogurt. The antibiotics can also inhibit the intestinal flora of young children who consume large quantities of such milk. Residual antibiotics can also provoke allergic responses in certain sensitive people.
Although the use of antibiotics to treat mastitis is for an obvious economic benefit, there is a countervailing economic loss to the dairyman from antibiotic residues, since the normal therapies involve infusions over one or two days, followed by milk discard times of two to four days. It is thus desirable to employ an antimicrobial material in the prevention and/or treatment of mastitis which does not leave unwanted residues. In addition, it is important that any broad-spectrum and short-lived antimicrobial does not provoke an inflammatory response in the udder, which would lead to an elevation of somatic cells (macrophage and neutrophilic white cells).
Accordingly, there is a need in the art to resolve the above problems. The present invention accomplishes these objectives, and provides other related advantages.